1. Field of the Invention
The present invention relates to a method of embodying all-optical XOR logic gate by using semiconductor optical amplifiers. More particularly, the present invention relates to a technique to embody all-optical XOR logic gate by utilizing the inverter characteristic of semiconductor optical amplifiers controllable with input currents, illumination signals, and pumping signals.
2. Description of the Related Art
In recent years, needs for high speed and large capacity of calculating systems have been increased. However, almost all calculation systems based on silicon material and electric signals have barriers in speed and capacity.
On the other hand, calculation systems using optical elements based on InP are coping with such barriers of speed and information processing capacity.
Generally, single optical logic elements such as AND, OR, XOR, NAND, NOR, and NXOR are integrated to constitute calculating systems. The integration technique is indispensable to calculation systems using optical signals.
Recently, researches have been focused on the XOR logic element development since XOR logic has various applications to communication purposes such as decision-making and packet switching (Refer to IEEE Photonics Technology Letters, Vol. 13, No. 7, pp. 750-752 (2001) by T. Fjelde, A. Kloch, D. Wolfson, B. Dagens, A. Coquelin, I. Guillemot, F. Gaborit, F. Poingt, and M. Renaud.). Examples include: XOR using Ultrafast Nonlinear Interferometer (UNI) presented by C. Bintjas, M. Kalyvas, G. Theophilopoulos, T. Stathopoulos, H. Avramopoulos, L. Occhi, L. Schares, G. Guekos, S. Hansmann, and R. Dall'Ara in IEEE Photonics Technology Letters, Vol. 12, No. 7, pp. 834-836 (2000); XOR using Tetrahertz Optical Asymmetric Demultiplexer (TOAD) presented by Pousite, Blow, Kelly, and Manning in Opt. Commun. 156, pp. 22-26 (1998); XOR using Sagnac gate presented by T. Houbavlis, K. Zoiros, A. Hatziefremidis, H. Avramopoulos, L. Occhi, G. Guekos, S. Hansmann, H. Burkhard, and R. Dall'Ara in Electronics Letters, Vol. 35, No. 19, pp. 1650-1652 (1999); and XOR using Interferometric Wavelength Converter (IWC) presented by T. Fjelde, D. Wolfson, A. Kloch, B. Dagens, A. Coquelin, I. Guillemot, F. Gaborit, F. Poingt, and M. Renaud in Elecronic Letters, Vol. 36, No. 22, pp. 1863-1864 (2000).
Aforementioned elements using UNI, TOAD, and Sagnac gate have the advantage of high operation speed but are difficult to apply to optical calculation systems requiring high density integration because their core element is optical fiber that is difficult to integrate with other elements.
On the other hand, optical logic elements using single Semiconductor Optical Amplifier (SOA) are not only stable, small-sized, and easy to combine with other optical elements but also have the merit of having independence on polarization and wavelength. (Refer to Elecronic Letters, Vol. 36, No. 22, pp. 1863-1864 (2000) by T. Fjelde, D. Wolfson, A. Kloch, B. Dagens, A. Coquelin, I. Guillemot, F. Gaborit, F. Poingt, and M. Renaud.)
A forementioned IWC is an element made by integrating these semiconductor optical amplifiers, but not suitable for large-scale fabrication due to its complicated fabrication process.
Moreover, since XOR logic elements disclosed so far depend on clock signal or continuous wave (CW) light, they need additional beam other than input signals A and B.